1. Field of the Invention
This invention relates to visual inspection method and apparatus for performing a visual inspection for contact lenses using an image pickup device to detect defects of contact lenses such as soil, foreign matters, scratches, breakage, peripheral damage, etc. of the contact lenses.
2. Description of Related Art
In order to perform a visual inspection for contact lenses to detect defects of the contact lenses such as soil, foreign matters, scratches, breakage, peripheral damage, etc., the following method has been conventionally utilized. That is, contact lenses are directly projected in an enlarging scale one by one by an optical projector for the visual inspection without being placed in a container (that is, under a condition that these are not protected from an external force), and an operator checks a projected screen to find out the defects.
For example, Japanese Laid-open Patent Application No. 63-48431 which is titled "Lens Inspection Device" discloses a technique in which an image (picture) of a lens is divided into a central part image and a peripheral (profile) part image to measure a binary signal time for each part image and then the quality of the lens (i.e., whether the lens is good or bad) is judged on the basis of the judgment as to whether the binary signal value is within a permissible range.
Furthermore, in a technique as disclosed in Japanese Laid-open Patent application No. 2-257007 which is titled "Inspection Device for Peripheral Chip of Contact Lens", the peripheral portion of a contact lens is imaged by an image pickup device to obtain a binary image of the contact lens, then the position coordinates of the peripheral portion are detected on the basis of the binary image by detection means, and then the least square quadratic approximation is performed on the basis of the detected position coordinates. Through this approximation method, the peripheral chip of the contact lens can be detected on the basis of the following parameters: the difference between the position coordinates detected by the detection means, which would be originally a very small value if the contact lens has no chip; the quadratic coefficient of the quadratic approximation curve; and the width of the imaged peripheral portion.
In a technique as disclosed in Japanese Laid-open Patent Application No. 4-305144 which is titled "Inspection Device for Peripheral Chip of contact Lens", the peripheral chip of the contact lens is detected by a contact lens detection means for converting an image of the contact lens into electrical signals, an image processing means for converting the electrical signal to image (picture) signals to extract only the peripheral portion of the contact lens, an arithmetical processing and judging means for processing the extracted portion to search a peripheral chip and judging the peripheral chip of the contact lens, and a transferring means for transferring the contact lens to a position at which the contact lens detection means can detect the contact lens.
Still furthermore, in a technique as disclosed in Japanese Laid-open Patent Application No. 4-321186 which is titled "Process and Device for Inspecting Optical Articles, particularly Optical Articles associated with Eyes, and Device for Illuminating Transparent Object Being Inspected", the image of an article being inspected is formed, and then defects of the imaged article being inspected is subjected to an image analysis to detect the defect. In the image analysis, a two-dimensional high-contrast image is formed to set an image area for a visualized defect, and then the defect image is compared with a threshold above "1".
In the conventional visual inspection devices for contact lenses as described above, the contact lenses has been inspected one by one using the optical projector or CCD image pickup device while they are not placed in containers as described above. Therefore, the inspected contact lenses are liable to be damaged (soiled, scratched or the like) during a period from the end of the visual inspection till the time when the contact lens is put into a storage container, and thus much attention must be paid to the handling of the contact lens. Particularly with respect to a soft contact lens, it is more liable to be soiled or scratched, and thus the visual inspection of a contact lens has been increasingly required to be performed while the contact lens is placed in a container (that is, under such a condition that the contact lens is protected from the external force).